This patch allocates snapshot memory for global reg, port regs, CQ, DQ,
IOST, ITCT.

When we fail to allocate memory for some registers, we free the memory
and set hisi_sas_debugfs_enable as 0 to stop loading debugfs from running.
Signed-off-by: Luo Jiaxing <luojiaxing@huawei.com>
Signed-off-by: John Garry <john.garry@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>